Is There An Optimal Gauge Length for Dynamic Tensile Specimens?

Rotbaum, Y.; Rittel, D.

doi:10.1007/s11340-014-9889-8

Cited by 19 publications

(8 citation statements)

References 15 publications

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“…The results obtained was in the same range of other previous work for similar combination [3,4] .The stress-strain curve show a small elastic response to the dynamic load while plastic deformation take place from the begging of the loading to the failure point.…”

Section: Resultssupporting

confidence: 86%

“…New simple method was proposed for measuring the material tensile behavior under high loading rates using a simple modification for SHPB arrangement and the Experimental results of stressstrain values were found to agree with previous work done by other researchers [3,4]. the result shows that bimetal junction can resultant up to 3 times of static load in case of dynamic load which indicate the suitability of usage of such junction in process subjected to dynamic load such as water hummer also the ductile nature of the fracture indicate the difficulty of catastrophic brittle fracture of the junction.…”

Section: Resultssupporting

confidence: 81%

“…Their setup utilized a "hat" type specimen sandwiched between a solid incident bar and a tubular transmitter bar. [3] prepared a modified version of the SHPB in which the load were applied using a 400 mm long tubular projectile and the air gun in an opposite position. However their setup was only capable of applying low magnitude force due to the nature of the tube projectile and motion difficulties.…”

Section: Introductionmentioning

confidence: 99%

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Measurement of Tensile Properties of Welded Dissimilar Material at High Strain Rate Using Split Hopkinson Pressure Bar Arrangement

Abdrahman

Khairaldien

Khalil

2017

JES. Journal of Engineering Sciences

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Modern industrial and constructional applications require clear understanding of engineering material behavior under dynamic loading conditions especially for junction with dissimilar material. The most accurate method available for studying dynamic behavior accurately Split Hopkinson, however the compression nature of the test hinder the usage of this technique of split Hopkinson pressure bars which was designed to characterize compressive load material behavior. Many trial were made to modify SHPB gain the capability of loading samples in uniaxial tension using different construction modifications. However most of these trails failed to provide the adequate condition of wave motions and neglected the losses due to geometrical arrangement. In this work a simple method was proposed and executed to produce a tensile wave in the Hopkinson bar and use it to measure the tensile properties of material. The uniaxial tension load was applied with the help of a double cone opposites to each other that transfer the compression wave into a tensile wave through two cone ends that hit a hollow cylinder with machine cone ends holes the widen when the bars hit it with a compression wave and transfer the compression wave into a tension wave. The specimen used was a bimetal welded specimen which was tested under loading rates up to 500 s-1. The results showed a similarity in performance compared to static test but at a much higher load and at very low plastic deformation. The microstructure examination of the broken specimen shows a small ductile fracture surface and in some loading rates a cup and cone formation tendency.

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Section: Resultssupporting

confidence: 86%

Section: Resultssupporting

confidence: 81%

Section: Introductionmentioning

confidence: 99%

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Measurement of Tensile Properties of Welded Dissimilar Material at High Strain Rate Using Split Hopkinson Pressure Bar Arrangement

Abdrahman

Khairaldien

Khalil

2017

JES. Journal of Engineering Sciences

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“…In order to prevent from specimen reloading, a momentum trap was brought initially in contact with the loaded flange of the incident bar, whose length was identical to that of the projectile bar. Further details of the experimental arrangement can be found in Rittel et al (2014) and Rotbaum and Rittel (2014). Moreover, a Kirana high speed digital camera was synchronized with the incident bar signals to record the deformation of the specimen during the loading process.…”

Section: Methodsmentioning

confidence: 99%

Necking evolution in dynamically stretched bars: New experimental and computational insights

Vaz-Romero

Rotbaum

Rodríguez-Martínez

et al. 2016

Journal of the Mechanics and Physics of Solids

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a b s t r a c tThis paper presents new results on dynamic neck evolution in steel bars of varying diameters. Dynamic tensile tests were carried out in a Kolsky apparatus using cylindrical steel specimens with various cross-section diameters ranging from 1.5 mm to 4 mm. A high speed digital camera was used to record the deformation of the specimen during the loading process. Video recording of the tests enabled accurate experimental measurements of the necking evolution, specifically its growth rate as a function of the diameter. The experiments show that increasing the specimen cross-section slows down the neck development. This behavior has been further investigated using two different kinds of numerical calculations: (1) axisymmetric finite element simulations and (2) one-dimensional finite difference computations. While the finite difference model only considers the normal stress along the longitudinal direction of the bar, the finite element model does not entail any simplification on the stress state of the specimen during the loading process. In agreement with the experiments, the finite element calculations show a decrease of the necking growth rate with the increase in the cross-section of the sample. On the contrary, the damping effect of the specimen cross-section on the necking evolution is not captured by the finite difference computations. We postulate that this result comes from the one-dimensional nature of the finite difference model. This work uncovers, by means of combined experiments and modelling, the key role played by stress multiaxiality in the growth rate of dynamic necks.

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“…However, they determine this effective length using numerical simulations. Rotbaum et al [9] suggest using long specimens, to keep the stress and strain distribution constant in a large part of the specimen prior to necking. In this way they are able to use the classical analysis with minimal error, but only for plastic strains of up to 3%.…”

Section: Introductionmentioning

confidence: 99%

Improving data interpretation from SHTB tests on ductile metals

Lindenfeld

Partom

2018

EPJ Web Conf.

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This work presents a methodology to calibrate a strength model for ductile metals, based on dynamic tension tests of relatively long Dog-Bone specimens conducted on a Split Hopkinson Tension Bar (SHTB). We address the main difficulties involved in conducting and interpreting such tests, namely the duration of the loading pulse needed to deform long specimens and the non-uniform stress and strain distributions along the specimen due to neck formation. The first issue is addressed by using the waves‘ reflections within the output bar, as explained below. When the first loading (tension) wave does not cause failure of the specimen, a reflected compression wave travels from the specimen‘s bar end to the free bar‘s end. Upon reaching the free end this latter compression wave is reflected again as a second tension wave, which travels back along the bar until it reaches the specimen and loads it the second time. This enables further deformation of the specimen, practically doubling the loading pulse duration without changing the striker‘s length. The second issue is addresses by using full numerical simulations of the experimental setup, including the striker, the bars and the specimen. This way, the full dynamic behaviour of the specimen is taken into account, eliminating the need to consider specimen equilibrium and taking into account the current strain rate in the specimen as it deforms. Hence, model calibration can be done from the very start of plastic deformation and without the need to keep the strain rate constant during deformation. As a result, it is possible to reliably calibrate the strength model considering necking and neck location, as well as plastic heating which is a significant factor in the plastic deformation of ductile metals.

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Is There An Optimal Gauge Length for Dynamic Tensile Specimens?

Cited by 19 publications

References 15 publications

Measurement of Tensile Properties of Welded Dissimilar Material at High Strain Rate Using Split Hopkinson Pressure Bar Arrangement

Measurement of Tensile Properties of Welded Dissimilar Material at High Strain Rate Using Split Hopkinson Pressure Bar Arrangement

Necking evolution in dynamically stretched bars: New experimental and computational insights

Improving data interpretation from SHTB tests on ductile metals

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